As an method for producing a semiconductor device, there is known conventionally molecular beam epitaxy (MBE) process which comprises causing solid raw material to be evaporated using a heater, electric beam and the like, and depositing the obtained vapor on a substrate in an ultra-high vacuum chamber made of stainless steel to thereby cause growth of crystal. However, because of the use of the solid material, vacuum condition of the vacuum chamber has to be released for replenishment of the material every time the material is used up, and it takes long time to put the inside of the vacuum chamber back to the ultra-high vacuum condition again, which intermits growth of crystal film to cause unevenness of crystal film quality. These are disadvantages of this method.
Therefore, a process which comprises supplying constitutive material of crystal in a gaseous state (gas source MBE) has been tried recently in order to remove the above-mentioned disadvantages. In this method, an apparatus provided by a principle as shown in FIG. 4 is employed, for example. That is, in the center portion of a vacuum chamber 1 of the apparatus, a heater 6 is hung from the top and a substrate holder 5 pasted with a substrate 2 with indium and the like is set below the heater 6. And plural kinds of gasses are supplied at the same time through material gas feeding pipes 9 and 10 positioned down below with heating the above-mentioned substrate holder 5 and substrate 2 by radiant heat to thereby be deposited on the reference numeral 2a (a surface of the substrate 2) and cause growth of crystal. The reaction is ordinarily put in practice at high vacuum of about 10.sup.-4 to 10.sup.-6 Torr, and vacuum drawing is conducted by a vacuum pump (not shown) communicating with a vacuum pipe 8. Because material can be supplied continuously in this method, release of vacuum condition is not required for replenishment of material as is used to be, so that high quality crystal thin film can be obtained in short time.
The above-mentioned gas source MBE process has no problem for producing compound semiconductor such as GaAs, InP, and the like. However, for producing Si based semiconductor such as Si, SiGe, and the like, it is found that reproducibility of crystal growth is damaged because Si begins to accumulate on the heater 6 and the substrate holder 5 when the pressure for Si crystal growth in the vacuum chamber 1 reaches about 10.sup.-5 Torr and Si accumulates radically at the vacuum of around 10.sup.-4 Torr, which is suitable pressure for crystal growth of Si, to hinder radiating heat from the heater. Also Si requires the temperature over 1100.degree. C. for film production and needs much more calorie than Ga (Film production temperature is 700.degree. C.) does. Particularly, heat efficiency of silicon wafer is even worse because of its high heat transmissivity. Therefore, the improvement of heat efficiency of the previous apparatus is strongly desired.
It is accordingly an object of the invention to provide an improved apparatus for gas source molecular beam epitaxy with excellent heat efficiency while no accumulation of Si appears on the heater and the like during production of Si based semiconductor.